Magnetic frustration in the cubic double perovskite Ba2NiIrO6

Abstract

Hybrid transition metal oxides continue to attract attention due to their multiple degrees of freedom (e.g., lattice, charge, spin, and orbital) and versatile properties. Here we investigate the magnetic and electronic properties of the newly synthesized double perovskite Ba2NiIrO6, using crystal field theory, superexchange model analysis, density functional calculations, and parallel tempering Monte Carlo (PTMC) simulations. Our results indicate that Ba2NiIrO6 has the Ni 2+ (t 6 2g e 2 g )-Ir 6+ (t 3 2g ) charge states. The first nearest-neighboring (1NN) Ni 2+ -Ir 6+ ions prefer a ferromagnetic (FM) coupling as expected from the Goodenough-Kanamori-Anderson rules, which contradicts the experimental antiferromagnetic (AF) order in Ba2NiIrO6. We find that the strong 2NN AF couplings are frustrated in the fcc sublattices, and they play a major role in determining the observed AF ground state. We also prove that the J eff = 3/2 and J eff = 1/2 states induced by spin-orbit coupling, which would be manifested in low-dimensional (e.g., layered) iridates, are however not the case for cubic Ba2NiIrO6. Our PTMC simulations show that when the long-range (2NN and 3NN) AF interactions are included, an AF transition with TN = 66 K would be obtained and it is well comparable with the experimental 51 K. Meanwhile, we propose a possible 2×2×2 noncollinear AF structure for Ba2NiIrO6.